1. Field of the Invention
The present invention relates to a pixel structure and a pixel array substrate, and more particularly, to a pixel structure and a pixel array substrate increasing aperture ratio, which is a technology of HannStar Ultra-high Aperture (HUA).
2. Description of the Prior Art
Liquid crystal display panels have been applied to portable products, such as notebook, PDA, etc. because of having the advantages of light weight, thin thickness, low power consumption and no radiation pollution, and thus, the liquid crystal display panels have been gradually replaced the cathode ray tube (CRT) screen of the laptop computer.
Conventional liquid crystal display panel is formed with the color filter substrate, the pixel array substrate and the liquid crystal layer, in which the liquid crystal layer is disposed between the color filter substrate and the pixel array substrate, and directions of the liquid crystal molecules in the liquid crystal layer can be rotated to control the pixel to display brightness or darkness. Please refer to FIG. 1, which is a schematic diagram illustrating a pixel structure of a pixel array substrate according to the prior art. As shown in FIG. 1, the pixel structure 10 includes a substrate 12, a thin-film transistor 14, a common line 16, a protection layer 18, a planarization layer 20, and a pixel electrode 22. The thin-film transistor 14 is disposed on the substrate 12, and includes a gate electrode 14a, a source electrode 14b, a drain electrode 14c, and a channel layer 14d. The common line 16 is disposed on the substrate 12. The protection layer 18 covers the thin-film transistor 14 and the substrate 12, and has a first opening 18a exposing the drain electrode 14c. The planarization layer 20 covers the protection layer 18, and has a second opening 20a corresponding to the first opening 18a and exposing the drain electrode 14c. The pixel electrode 22 is disposed on the planarization layer 20 and electrically connected to the drain electrode 14c through the first opening 18a and second opening 20a. Furthermore, the common line 16 overlaps the pixel electrode 22, so that the common line 16, the pixel electrode 22, the protection layer 18, and the planarization layer 20 form a storage capacitor.
However, when the first opening 18a is aligned to the drain electrode 14c of the thin-film transistor 14, there is an alignment deviation between them. Also, when the second opening 20a is aligned to the first opening 18a, there is another alignment deviation between them. Furthermore, when the pixel electrode 22 is formed to cover the second opening 20a, there also is another alignment deviation between them. Since the alignment deviations among the first opening 18a, the second opening 20a and the pixel electrode 22 affect one another, a size of the connecting structure for electrically connecting the pixel electrode 22 and the drain electrode 14c of the thin-film transistor 14 is affected by the alignment deviations. Thus, in order to make the pixel electrode 22 be in contact with the drain electrode 14c through the first opening 18a and second opening 20a, a second feature length L2 of the connecting structure should be designed to be larger than a first feature length L1 of the first opening 18a and the same as 4 to 8 times of the first feature length L1 of the first opening 18a, for example, 20 microns to 28 microns. The size of the connecting structure 24 for connecting the pixel electrode 22 and the drain electrode 14c will affect the area of the pixel electrode 22 for displaying, and the aperture ratio of the pixel structure 10 is accordingly limited.
Therefore, with the increase of the image resolution of the pixel array substrate, to raise the aperture ration of the pixel structure is an objective in this field.